An energy management system (EMS) is a system of computer implemented tools used by operators of electric utility grids to monitor, control, and optimize the performance of the generation and/or transmission of an energy delivery system. In other words, an EMS optimizes, supervises and controls the transmission grid and generation assets. The monitoring and control functions are known as “supervisory control and data acquisition” (SCADA). Control of such a system involves autonomous automatic control actions by the EMS to arrest deviations in power system frequency whenever imbalances arise between load and generation.
Primary frequency control actions include governor response, load damping, and voluntary frequency-responsive load control, all of which contribute to frequency response. Secondary frequency control involves centrally coordinated control actions by the EMS to return frequency to its scheduled value. The control actions are deployed both during normal operations and after primary frequency control resources have arrested frequency imbalance following major disturbances. Secondary frequency control actions include generation (or load) that responds to automatic generation control (AGC) signals or to operator dispatch commands. AGC is often referred to as “regulation” service.
There are a number of unique challenges to supplying electricity: production must be simultaneous with demand; demand varies greatly over the course of a day, week, and season; the costs of operating different types of generating units vary greatly; and both expected and unexpected conditions on the transmission network affect which generating units can be used to serve load reliably. Conventional security constrained economic dispatch (SCED) is an optimization process that takes into account these factors in selecting the generating units to dispatch, in order to deliver a reliable supply of electricity at the lowest cost possible under given conditions.
There are typically two stages, or time periods, to the economic dispatch process: day-ahead unit commitment (i.e., planning for tomorrow's dispatch) and unit dispatch (i.e., dispatching the system in real time). In the day-ahead unit commitment stage, operators must decide which generating units should be committed to be on-line for each hour, typically for the next 24-hour period (hence the term “day-ahead”), based on the load forecast. In selecting the most economic generators to commit, operators must take into account each unit's physical operating characteristics, such as how quickly output can be changed, maximum and minimum output levels, and the minimum time a generator must run once it is started. Operators must also take into account generating unit costs, such as fuel and non-fuel operating costs and costs of environmental compliance.
In addition, forecasted conditions that can affect the transmission grid must also be taken into account to ensure that the optimal dispatch can meet load reliably. This is the “security constrained” aspect of the commitment analysis. In other words, the optimization process is constrained by requirements that insure the system functions safely and reliably. Factors that can affect grid capabilities include generation and transmission facility outages, line capacities as affected by loading levels and flow direction, and the weather. If the security analysis indicates that the optimal economic dispatch cannot be carried out reliably, relatively expensive generators may have to be used in place of less expensive to operate units or resources.
In the real time unit dispatch stage, operators must decide in real time the level at which each available resource (e.g., as identified during the day-ahead unit commitment stage) should be operated, given the actual load and grid conditions, such that reliability is maintained and overall production costs are minimized. Actual conditions will vary from those forecasted in the day ahead commitment and operators must adjust the dispatch accordingly. In addition, transmission flows must be monitored to ensure flows stay within reliability limits and voltage within reliability ranges. If transmission flows exceed accepted ranges, the operator must take corrective action, which could involve curtailing schedules, changing the dispatch, or shedding load.
The proliferation of renewable energy and particularly wind power, present significant challenges to EMSs and energy market management systems (EMMS). Because these energy sources are frequently intermittent, it can be difficult to incorporate the energy they produce into existing power distribution systems that are designed to provide continuous, reliable power. Thus, there is a significant need to provide systems, methods and apparatus for improved energy management systems with security constrained dynamic dispatch for wind power management.